The present invention relates generally to a drive arrangement and, more particularly, to such an arrangement which is used for driving elements such as movable step plates and/or doors on transport vehicles so as to facilitate passenger access to such vehicles.
It is known in the prior art to provide a drive arrangement for actuating doors which are to turn, fold or pivot relative to the transport vehicle. A motor is employed to operate two crank arms, each of which is connected to a push rod provided with a slip clutch. One push rod is connected to a shaft by means of a link, the other rod is connected with a hollow shaft which surrounds the first-mentioned shaft. Each of these shafts has another link which is in turn connected to another push rod that is connected to a double folding door. Two motor cam switches are provided to actuate the motor on or off.
However, this prior art arrangement is disadvantageous because it does not permit manual operation of the doors. In case of an emergency, the doors can be manually opened only with great difficulty if one succeeds in overcoming the force of the slip clutch. Even so, after such manual manipulation, the cam switch arrangement for controlling the motor will now be out of proper alignment. If one desires to restart the motor, one must reset the cam parts back to their original predetermined position relative to each other. Not only are such prior art arrangements complex in their construction so that the resetting of the cam switch parts is a lengthy time-consuming operation, but also the various mechanical parts of such arrangements are particularly prone to failure due to their increased wear.